1. Field of the Invention
The present invention relates to a travelling vehicle system for carrying a cargo along a track to transfer the cargo to a rack or the like.
2. Description of the Related Art
There has hitherto been known a travelling vehicle system for allowing a travelling vehicle to travel along a rail (one example of a track) hung on a ceiling, to carry a cargo in the vicinity of the ceiling. The travelling vehicle includes a lift stage liftably hung by means of a hanging member. The travelling vehicle transfers the cargo by lowering the lift stage to a placement member of a rack arranged along a travelling route of the travelling vehicle.
The track is installed in accordance with arrangement of the rack. The travelling route formed by the track typically includes a divergence part and a merging part (e.g., International Publication WO2009/142051). In the divergence part and the merging part, a switching track for connecting one track to one of a plurality of tracks is provided. The travelling vehicle selects a travelling route in accordance with a cargo loading/unloading instruction, to load and unload a cargo.
However, when the plurality of travelling vehicles are allowed to travel, there may arise a need for waiting before the switching track in order to obtain a permission to enter the switching track, which is problematic. From the viewpoints of efficiency in loading/unloading a cargo, reduction in operation time, and the like, it has been required to allow the travelling vehicle to travel more smoothly.